1. Field of the Invention
This invention relates to an electrophotographic apparatus comprising an electric charge holding member supported by at least an electrically conductive body, a developing device for developing an electrostatic latent image produced on said electric charge holding member into a visible image, a transfer device including a transfer roller arranged in contact with the electric charge holding member, and an image receiving paper feed means for feeding an image receiving paper through a toner image transfer portion where said electric charge holding member makes contact with the transfer roller and operative to repeat developing and transfer steps with respect to the electrostatic latent image once produced on the electric charge holding member to form the same picture image on a plurality of image receiving papers.
2. Description of the Prior Art
Such conventional electrophotographic apparatus has the disadvantage that when the apparatus operates under a high humid condition or use is made of an image receiving paper whose resistance value is low due to its humid absorption property or the like, the transfer efficiency of the toner image becomes considerably low, and as a result, it is impossible to obtain a good picture image copy. In order to eliminate such drawback, another electrophotographic apparatus has been proposed which is constructed such that a bias voltage having a polarity which is the same as that of a bias voltage applied to the transfer roller is applied to an image receiving paper guide located near the transfer roller. But, such conventional electrophotographic apparatus has a number of disadvantages. In the first place, in order to always bring the image receiving paper into contact with the guides and transfer roller which are applied with the bias voltage, the bias voltage must be applied to these guide and roller widely distant apart from each other and these guide and roller must be insulated from the apparatus main body which is applied with ground potential, and as a result, the apparatus is complex in construction. Secondly, if the members applied with the bias voltage are located near the toner transfer portions, more or less deviation of the image receiving paper from a predetermined feed path results in a band-shaped or island-shaped picture image copy which is irregular in concentration. Third, if the image receiving path is made narrow in width in order to improve contact between the guides applied with the bias voltage and the image receiving paper, the image receiving path becomes jammed with the image receiving paper. Finally, if the resistance value of the image receiving paper is lowered, an electric charge is injected from the transfer roller and image receiving paper feed path member applied with the bias voltage through the image receiving paper having low resistance value into the photosensitive drum, thereby inducing fog on the non-picture image portion of the image receiving paper at each transfer step in the case of obtaining a plurality of copies.